I got the impression that GL's poor quality was largely the result of studio interference, so I wouldn't be inclined to blame the writer so much for that. So, in the interest of fairness, what else has this guy written?

It had four writers, and the part where the movie failed was, the producers didn't know it should have visual design. Not that the script was good, but usable it was, now whether he can make something tolerable for this seemingly trickier project, who knows. Prometheus worked just fine, even if the script wasn't good.

Yeah, if it's what I think it is (a quasi modern/parallel world retelling of the biblical story of David?), I really enjoyed it while it lasted.

Everything I've heard/read about GL screams multiple re-writes and a studio not knowing how to handle what they've got, or even really understand the source material. Indeed, the upcoming 'World War Z' has a similar odor to it. Under those circumstances, a writer is just a hired gun and by no means solely responsible for the end product.

Indeed, a number of times in recent years, I've been pleasantly surprised at the high quality of certain films made by people who's writing and/or directing credits up to that point have ranged from mediocre to utterly dire. So I put less and less stock in such things when considering my expectations for a new film.

Still, given the frustrating disappointment that was Prometheus (it honestly would have been better if the dropped all links with with Alien...and got a JCB to fill in those gaping plot holes) I'm very wary of Ridley doing a sequel to Blade Runner. At least with Alien there was potential for more story telling and a compelling mystery extant in the first film (who were the space jockeys?) that was never addressed in any of the cinematic sequels or spin-offs.
While as the excellent 1997 video game proved, there are certainly more storytelling opportunities in the world of Blade Runner, a direct sequel just doesn't feel right.